Watt, James (1736–1819)

Scottish engineer and inventor. His first major invention was a steam
engine with a separate condenser and thus far greater efficiency. For
the manufacture of such engines he entered partnership with John Roebuck
and later (1775), more successfully, with Matthew Boulton.
Between 1775 and 1800 he invented the sun-and-planet gear wheel, the double-acting
engine, a throttle valve, a pressure gauge, and the centrifugal governor – as well as taking the first steps toward determining the chemical
structure of water. He also coined the term horsepower and was a founder member of the Lunar
Society.

Like earlier steam engines, James Watt's engine of the 1770s also condensed the steam with water, but in a separate condenser (1). This technique, and that of admitting steam to both sides of the piston (2), greatly increased the efficiency of the steam engine. Pushing the piston in both directions made it double-acting. Watt soon adapted it to produce rotary motion, used for machines other than pumps.